Personally, I would find bedding that you like that will set the stage for that color scheme and go from there. Have you seen bedding that you like?

You will probably have more options in black or black and white than mustard. But I really like this black and gold comforter.

Because the furniture and room both look dark, I'd be tempted to choose lighter bedding colors.

With a black , gold, mustard and white scheme I would concentrate on textures. You can get all sorts of cool textures with solid color quilts. You could also include warm creams and charcoals. Layer the bed in whites and warm creams. Add some decorative pillows, drapes and a throw to the room in patterns or solids in velvet, silky, fur or open weave material in charcoal, black, white or vibrant mustard. Maybe a pinch of leopard? Go sensually basic but luxurious on your main bedding & add the zing to the rest.